Process for the production of hydrocarbons from hetero-substituted alkanes

ABSTRACT

A product comprising hydrocarbons having at least 2 carbon atoms is produced by contacting a monohalomethane at elevated temperature, e.g. 200° to 600° C., with a synthetic crystalline aluminosilicate zeolite having a silica to alumina molar ration of at least 12:1 and containing cations of either hydrogen, copper or a metal capable of forming an amphoteric oxide, which cations are introduced either by exchange and/or by deposition, provided that when the cation is hydrogen the zeolite is Theta-1. At temperatures below 330° C. the product predominantly comprises aliphatic hydrocarbons, of which a substantial proportion is isoalkanes and isoalkenes.

The present invention relates to a process for the production ofhydrocarbons from hetero-substituted alkanes.

The forecast longer-term shortage of petroleum has in recent yearsstimulated research into the production of chemicals and fuels fromother raw materials. In particular both coal and natural gas, of whichthere are vast reserves, have been under consideration because both arereadily converted by well established technology into a mixture of gasescomprising carbon monoxide and hydrogen, conventionally referred to assynthesis gas, which in turn can be converted into methanol. Methanol isa useful intermediate for the production of valuable chemicals, forexample acetic acid, ethanol, esters, acetic anhydride, etc., and inrecent years its use has been proposed both as a gasoline blendingcomponent and as a feedstock for the production of liquid gasoline rangehydrocarbons by conversion over synthetic crystalline aluminosilicatecatalysts, see for example U.S. Pat. No. 4,138,442 (Mobil).

In U.S. Pat. No. 3,894,107 (Mobil) there is described a process forconverting an aliphatic organic compound of the formula R-X where X isat least one of halogen, oxygen, sulphur or nitrogen to a productcomprising a complex mixture of compounds including hydrocarboncompounds having a greater numer of carbon atoms than the organiccompound reactant, a higher ratio of carbon atoms to heteroatoms thanthe organic compound reactant and a longest carbon to carbon chainlength which is longer than the longest carbon chain length of theorganic compound reactant by contacting the compound of formula R-X witha crystalline aluminosilicate zeolite having a silica to alumina ratioof at least about 12 and a constraint index of about 1 to 12. It isfurther stated that the zeolite may be in the hydrogen form or it may bebase exchanged or impregnated to contain ammonium or a metal cationcomplement, of which the latter may be a cation of the metals of theGroups I through VIII of the Periodic Table. No specificcation-exchanged form of the zeolite is identified as being desirablefor the conversion of any of the reactants embraced by the formula R-X,nor indeed is any specific cation-exchanged form of the zeolite said tobe desirable for the conversion of compounds of the formula R-X as ageneric class. The Examples illustrate only the use as catalyst of azeolite in the hydrogen form and 24 of the 26 Examples are devoted toalkanol conversions, the remaining two being directed to methylmercaptan conversion and tri-n-butylamine conversion. Of those Examplesdirected to alkanol conversion, the majority are devoted to the use ofmethanol as the feedstock.

U.S. Pat. No. 3,894,104 describes a process for converting a feedcomprising compounds of the type (R)_(n) -X where R is a lowerhydrocarbon moiety having 1 carbon atom, X is a hetero moiety selectedfrom the group consisting of oxygen, hydroxyl, sulphur, nitrogen,halogen and cyanide and n is a number up to the valence of X, to othercompounds having a higher ratio of R to X than in the feed by contactingsuch feed with a crystalline aluminosilicate zeolite catalyst, having asilica to alumina ratio of at least about 12 and a constraint index ofabout 1 to 12, at an elevated temperature of about 500° to about 750° F.at a space velocity of about 0.1 to 50 LHSV; the improvement, whereby aproduce a product which is predominantly normally liquid hydrocarboncontaining a larger proportion of aromatics, which comprises utilizingas said catalyst said zeolite which has been modified by theincorporation therewith of at least one metal of Groups Ib, IIa, IIb,IIIa, IVa and VIII of the Periodic Table. Representative feeds are said(column 5, lines 33 to 38) to include alcohols, particularly methanol,ethers, particularly dimethyl ether, ketones, particularly acetone andanalogous and homologous materials such as mercaptans or amines, inadmixture with each other and/or in admixture with other materials. Thespecific metals are incorporated in the catalyst for the purpose ofincreasing the aromatics content of the product. All 25 Examples aredirected to the conversion of methanol.

An alternative approach to the conversion of methane, which forms theprincipal component of natural gas, to hydrocarbons in the gasolineboiling range is to convert the methane to monohalomethane andthereafter to catalytically convert same to hydrocarbons. This route ispotentially more attractive than the methanol route because iteliminates one step in the process in that to produce the methanolfeedstock the methane must first of all be converted to synthesis gaswhereas methane can be converted directly with high selectivities tomonohalomethane. Moreover, the hydrogen halide produced as a by-productof the monohalomethane conversion can be recycled to the monohalomethaneproduction process, whereas the by-product of the methanol conversionprocess is not so utilisable. The chemistry of the conversion ofmethanol, and alcohols in general, as compared with monohalomethanesdiffers considerably, for example at low temperatures methanol isconverted to dimethyl ether whereas this reaction is not possible formonohalomethanes. Another significant difference is that in the case ofmethanol conversion water is co-produced, whereas the conversion ofmonohalomethanes co-produces hydrogen halides which are known todealuminate crystalline aluminosilicate zeolite structures leading toframework collapse and irreversible loss in catalytic activity.Dealumination would be anticipated to be more serious in the presence ofhydrogen halides than in the presence of water. Conclusions drawn fromthe prior art regarding methanol conversion are therefore notnecessarily applicable to monohalomethane conversions.

Japanese patent publication No. J55073-619 teaches that methane can beconverted into methyl chloride and thereafter dehydrochlorinated using azeolite to produce hydrocarbons having at least 2 carbon atoms. Thezeolite employed is a silicate mineral consisting of SiO₂, Al₂ O₃ andalkali metal or alkaline earth metal.

We have now found that monohalomethanes can be efficiently converted tohydrocarbons in the gasoline boiling range and moreover, within acertain temperature range, the selectivity to desirable aliphatichydrocarbons and particularly to isoalkanes and isoalkenes can be highusing cation-exchanged synthetic crystalline aluminosilicate catalysts.Furthermore, the activity of the catalyst depends on the nature of thezeolite employed and upon the nature of the cation. Moreover, we havesurprisingly found that the activity of the catalysts can be maintainedfor substantial periods and that some at least of the catalysts can beregenerated.

Accordingly, the present invention provides a process for the conversionof a monohalomethane to a product comprising hydrocarbons having atleast 2 carbon atoms which process comprises contacting themonohalomethane at elevated temperature with a synthetic crystallinealuminosilicate zeolite having a silicate to alumina molar ratio of atleast 12:1 and containing cations of either hydrogen, copper or a metalcapable of forming an amphoteric oxide, which cations are introducedeither by exchange and/or by deposition, provided that when the cationis hydrogen the zeolite is Theta-1, as described and claimed in EuropeanPat. No. 57049B.

As regards the monohalomethane, the halo-moiety may suitably be chloro-or bromo-, preferably chloro-. Mixtures of monohalomethanes and/ormixtures of monohalomethane with other monohaloalkanes, for examplemonohaloethane, may also be employed. The monohalomethanes may be usedin substantially pure from or may be admixed with their polyhalogenatedanalogues or with inert diluents, nitrogen, hydrogen, oxygen, air,carbon oxides or hydrocarbons. As regards mixtures of polyhalogenatedmethanes and monohalomethanes, the amount of the polyhalogenated methanewhich can be tolerated in the mixture will depend upon the degree ofhalo-substitution, the nature of the zeolite and the nature of thecation. Thus, for example, using a mixture of monochloromethane anddichloromethane as the feed and a tin-exchanged ZSM-5 type crystallinealuminosilicate zeolite as catalyst, the maximum amount ofdichloromethane which can be tolerated in the feed is about 40% v/v. Itis of course preferred to operate with proportions of dihalomethaneconsiderably less than the critical amount. Monohalomethanes maysuitably be obtained by halogenation or oxyhalogenation of methane, ormore preferably, methane in admixture with ethane and/or propane in theform, for example, of natural gas. Suitable processes for selectivelyproducing monohalomethanes are described in our copending UK applicationpublication No. 212024914 (BP Case No. 5350) and our copending Europeanapplication publication No. 0117731 (BP Case No. 5538), the subjectmatter of which is incorporated by reference herein.

Any synthetic crystalline aluminosilicate zeolite having a silica toalumina molar ratio of at least 12:1, preferably from 15:1 to 150:1,even more preferably from 20:1 to 100:1, may be employed. Suitablesynthetic crystalline aluminosilicate zeolites include Theta-1 asdescribed in EP-A-No. 57049; ZSM-4 as described in UK Pat. Nos.1,117,568; 1,227,294; 1,297,256; and 1,321,460; ZSM-11 as described inU.S. Pat. No. 3,709,979; ZSM-5/ZSM-11 as described in U.S. Pat. No.4,229,422; ZSM-35 as described in U.S. Pat. No. 4,016,245; ZSM-34 andzeolite Nu-1 as described in GB-A-No. 1,559,367. Preferred syntheticcrystalline aluminosilicates are those designated as MFI zeolites in theatlas of Zeolite Structure Types by W. M. Meier and D. H. Olson,published by the Structure Commission of the International ZeoliteAssociation and Theta-1. Specific MFI-type zeolites which may be usedand processes for their production are described in for example U.S.Pat. Nos. 3,702,886; 3,709,979; 4,205,053; 4,166,099; 4,139,600 and4,151,189; UK Pat. Nos. 1,365,318 and 1,567,948 and EP-A-Nos. 2899 and2900, all of which utilise an organic base in their preparation.Alternatively, MFI-type zeolites may be synthesised from gels which arefree from organic bases as described in for example EP-A-No. 30911, U.S.Pat. No. 4,199,556 and GB-A-No. 2,018,232.

The crystalline aluminosilicate designated Theta-1 has the followingcomposition in term of the mole ratios of the oxides:

    0.9±0.2M.sub.2/n O:Al.sub.2 O.sub.3 :xSiO.sub.2 :yH.sub.2 O

where M is at least one cation having a valence n, x is at least 12 andy/x is between 0 and 25, said aluminosilicates in the calcinedhydrogen-form having an X-ray diffraction pattern as set forth in TableA hereinafter.

                  TABLE A                                                         ______________________________________                                                               Relative intensity                                     2 theta       d-spacing                                                                              100 × I/I.sub.o                                  ______________________________________                                         8.15 ± 0.5                                                                              11.5-10.2                                                                              50 to 100                                              10.16 ± 0.5                                                                              8.29-9.14                                                                              5 to 25                                                12.77 ± 0.5                                                                              7.20-6.66                                                                              10 to 20                                               16.36 ± 0.5                                                                              5.58-5.25                                                                              5 to 15                                                19.42 ± 0.5                                                                              4.68-4.45                                                                              5 to 15                                                20.35 ± 0.5                                                                              4.47-4.26                                                                              50 to 100                                              24.22 ± 0.5                                                                              3.75-3.60                                                                              50 to 100                                              24.65 ± 0.5                                                                              3.68-3.54                                                                              30 to 90                                               25.75 ± 0.5                                                                              3.52-3.39                                                                              15 to 45                                               35.63 ± 0.5                                                                              2.55-2.48                                                                              15 to 40                                               ______________________________________                                         scanned up to 2 theta = 36.                                              

The aluminosilicate may suitably be prepared by forming a mixture of allthe reactants, by simply mixing them together while maintaining themixture suitably at a temperature between 0° and 100° C., preferablybetween 20° and 60° C., until a homogeneous gel is formed andcrystallising the mixture so-formed at a temperature above 70° C.,preferably between 100° and 220° C., for a period of at least 2 hours,preferably for from 6 to 240 hours. Further details regarding thecrystalline aluminosilicate and its method of preparation may be foundin the aforesaid European Pat. No. 0057049, which is incorporated byreference in this specification.

As prepared the aforementioned crystalline aluminosilicate will almostcertainly contain cations other than those associated with their crystalstructures, for example they may contain either alkali metal and/oralkaline earth metal cations, organic nitrogen cations or ammoniumcations and possibly they may also contain organic bases or acidsdeposited in the pores and on the surface thereof, depending on theirmethod of preparation. In order to produce catalysts which are active inthe process of the present invention it is necessary either to exchangesome or all of the exchangeable cations of the crystallinealuminosilicates as prepared with other cations and/or deposit cationsthereon.

Using zeolites other than Theta-1, activating cations are cations ofcopper or of metals capable of forming an amphoteric oxide, anamphoteric oxide being regarded in simple terms as an oxide whichexhibits both acidic and basic properties. Metals capable of formingamphoteric oxides include for example beryllium, titanium, zirconium,hafnium, iron, cobalt, rhodium, silver, gold, zinc, aluminium, gallium,indium, silicon, germanium, tin, lead, pollonium and uranium. Of theaforesaid metals, zinc, gallium and silver are preferred at lowertemperatures, for example 200° to 260° C. Although Theta-1 may beactivated with at least one of the aforesaid cations, it is preferred toactivate the Theta-1 zeolite with hydrogen ions. We have found that thehydrogen form of Theta-1 is a more active catalyst than the hydrogenform of the MFI zeolite.

Cation-exchange may be accomplished using conventional ion-exchangetechniques. Deposition of the cation(s) may be accomplished byimpregnation or precipitation, or by any other technique. Deposition ispreferably effected by impregnation with a solution of a suitablecompound, for example a metal salt, which almost inevitably isaccompanied by exchange of exchangeable cations with other cations.Using cation-exchange, it is preferred to exchange substantially all theoriginal exchangeable cations. Using deposition the amount of metal ormetals deposited may suitably be up to 25% w/w, preferably from 0.1 to15% w/w calculated as metal(s) and based on the total weight of thecatalyst.

It is preferred to calcine the crystalline aluminosilicate afterintroduction of the replacing cations and optionally also beforeintroduction of the replacing cations. Calcination may suitably beeffected by heating, suitably in a stream of air, oxygen, inert gas orhydrogen, or any combination thereof at a temperature in the range from200° to 600° C., or above, for at least 0.5 hr.

The process for the conversion of monohaloalkane to hydrocarbons maysuitably be effected at an elevated temperature in the range from 80° to600° C. The pressure may suitably be atmospheric pressure, though higherand lower pressures may be employed if desired. Within the temperaturerange 80° to 600° C., aromatic hydrocarbons are not formed insignificant proportions below about 330° C. Below 330° C.,monohalomethanes are converted to a hydrocarbon product predominantlycomprising aliphatic hydrocarbons and, surprisingly, it is found that asubstantial proportion of the aliphatic hydrocarbons are isoalkanes andisoalkenes, which are highly desirable components of chemicalsfeedstocks and gasoline blending additives. It is preferred, for theproduction of aliphatic hydrocarbons, to operate in the temperaturerange 200° to 330° C., for example from 200° to 260° C. It may be notedby way of contrast that in the temperature range 200° to 260° C. andeven higher, for example 327° C., methanol would be converted todimethyl ether.

Although the process may be operated batchwise, it is preferablyoperated in a continuous manner. The Gas Hourly Space Velocity (GHSV)defined as the volume of reactant gas at STP per volume of catalyst perhour for continuous operation may suitably be in the range from 1 to10,000 vol/vol/hour. The process, may for example, fit into a processscheme whereby methane, optionally admixed with ethane and/or propane,is fed to a first zone wherein it is halogenated and/or oxyhalogenatedto produce monohalomethane at a selectivity based on methane fed ofgreater than about 80%, the monohalomethane and any monohaloethaneand/or monohalopropane so-produced is separated and passed as feed tothe process of the present invention and thereafter the hydrocarbonproduct is separated from the co-produced hydrogen halide(s), thehydrogen halide(s) either being recycled to the oxyhalogenation or beingoxidised and the halogen(s) so-produced being recycled to thehalogenation.

The catalyst in the process of the present invention may be employed inthe form of a fixed bed or a fluidised bed.

The process of the present invention will now be further illustrated byreference to the following Examples.

In a number of the Examples the terms "iso-content" and "aliphaticcontent" will be employed. The term "iso-content" is an indication ofthe minimal molar amount (%) of isoalkanes/isoalkenes present as part ofthe total C₄ -C₁₁ aliphatic hydrocarbon content. The term "aliphaticcontent" refers, on a similar basis, to the minimal amount of aliphatichydrocarbons present in the total C₃ -C₁₄ aliphatic and aromatichydrocarbon product composition. The "Al/Ar" ratio refers to the ratioof selectivities of C₂ ⁺ -aliphatic to C₆ ⁺ -aromatic hydrocarbons.These are terms defined in a manner such as to give a clear indicationof the variation in product spectra.

EXAMPLES 1 TO 4

Monochloromethane was fed continuously to a reactor containing thecation-exchanged form specified in Table 1 of the synthetic crystallinealuminosilicate zeolite ZSM-5 having a silica to alumina molar ratio of41:1. The reactor was heated externally by means of an electric furnaceand the heated zone was maintained at the temperature specified. Theapplied GHSV in per hourly units as STP are shown in Table 1. Theproduct stream was analysed by on-line gas chromatography.

The composition of the product streams, excluding unreactedmonohalomethane and hydrogen chloride, are shown in Table 1 togetherwith a summary of experimental details.

With reference to Table 1, no aromatic hydrocarbons were obtained usingthe metal cation-exchanged form of the ZSM-5 zeolite under theconditions of the experiments. The aliphatic hydrocarbon product had ahigh iso-content.

Comparison Test A

The procedure of Examples 1 to 4 was repeated using the hydrogen form ofthe ZSTM-5 zeolite as used in Examples 1 to 4 and using the specificconditions shown in Table 1.

This is not an example according to the invention because the hydrogenform of the zeolite was employed. It demonstrates that under theconditions of the experiment lower conversions are obtained using thehydrogen form of the zeolite.

Comparison Test B

The procedures of Examples 1 to 4 was repeated using the hydrogen formof the ZSM-5 zeolite back-exchanged with sodium cations (15%) and usingmethanol as the feed in place of monochloromethane at a comparableLiquid Hourly Space Velocity. The major product (91% conversion) wasdimethyl ether.

This is not an Example according to the present invention becausemethanol and not a monohalomethane was used as feed. It is provided forthe purpose of highlighting the difference in chemical terms betweenmonohaloalkanes and alkanols. Under the conditions employed, methanolforms mainly its condensation adduct, dimethyl ether, and small amountsof C₂ -C₃ hydrocarbons, whereas monochloromethane forms mainly C₄ -C₁₁aliphatic hydrocarbons.

EXAMPLES 5 TO 13

The procedure of Examples 1 to 4 was repeated using the conditions andthe cation-exchanged form specified in Table 2 of the ZSM-5 zeolite asused in Examples 1 to 4.

The composition of the product streams, excluding unreactedmonochloromethane and hydrogen chloride, are shown in Table 2 togetherwith a summary of experimental details.

It can be seen from Table 2 that operation at the higher temperaturesincreases the monochloromethane conversions, whilst producing a highlyaliphatic hydrocarbon product containing a high proportion ofiso-hydrocarbons. The Al/Ar ratio in, for example, Examples 6 and 10 wasrespectively 6.4 and 7.6 indicating a high aliphatic content of theproduct stream. Under similar conditions with methanol as feed (327° C.;1 h⁻¹ WHSV) over the sodium-exchanged zeolite (88% exchange) only lowconversion (1%) to hydrocarbon products was observed, the bulk of theproduct (94% conversion) being dimethyl ether.

In the case of Example 5 (Cu-exchanged form) the monochloromethaneconversion declined (to 70% conversion) after 18 hours on stream. Thiscompares with a drop in conversion (from 89% to 24%) after 9 hours onstream using the hydrogen form of the zeolite (327° C.; 200 h⁻¹) and isan indication of the improved stability of the catalysts of the presentinvention. Furthermore, the activity of the Cu-exchanged zeolite wasrestored to its original value by regeneration, whereas this was not thecase for the hydrogen-exchanged zeolite.

EXAMPLES 14 TO 19

The procedure of Examples 1 to 4 was repeated using the feedcompositions and cations as shown in Table 3.

The composition of the product streams, excluding unreacted methylchloride and hydrogen chloride, are shown in Table 4 together with asummary of experimental details.

Comparison Tests C and D

The procedure of Examples 1 to 4 was repeated using the feedcompositions and cations as shown in Table 3.

The composition of the product streams, excluding unreacted haloalkaneand hydrogen chloride, are shown in Table 4, together with a summary ofexperimental details.

These are not Examples according to the invention and are included forthe purpose of demonstrating that when the dichloromethane content ofthe feed mixture is greater than about 40% v/v hardly any conversion tohigher hydrocarbons is obtained.

EXAMPLES 20 TO 24

The procedure of Examples 1 to 4 was repeated using, in place of thecation-exchanged ZSM-5 zeolite as used in those Examples, variouscation-exchanged forms, as specified in Table 5, of a Theta-1 zeoliteprepared as described in the aforesaid European Pat. No. 57049B.

The composition of the product streams, excluding unreactedmonochloromethane and hydrogen chloride are shown in Table 5 togetherwith a summary of experimental details. In Table 5 is included thecorresponding data for Comparison Test A, for comparison purposes.

                  TABLE 1                                                         ______________________________________                                                  Example                                                                                               Comp.  Comp.                                                                  Test   Test                                           1    2      3      4    A      B                                    ______________________________________                                        Aliphatics                                                                    C.sub.1     3      2      3    1    0                                         C.sub.2 's  trace  1      0    1    0      43                                 C.sub.3 's  23     11     11   14   8      29                                 C.sub.4 's  56     60     67   64   68     14                                 C.sub.5 's-C.sub.11 's                                                                    18     26     19   20   24     14                                 Aromatics                                                                     C.sub.6 -C.sub.14 's                                                                      0      0      0    0    0      0                                  Conversion  60     21     9    24   7      9.sup.b                            Zeolite Form                                                                              Zn     Ag     Sn   Ga   H      Na                                 Temp/° C.                                                                          227    227    227  227  227    224                                GHSV/h.sup.-1                                                                             55     73     52   51   57     1.sup.a                            iso-content 80     87     92   85   100    82                                 aliphatic content                                                                         100    100    100  100  100    100                                ______________________________________                                         Note-                                                                         .sup.a = Liquid Hourly Space Velocity                                         .sup.b = Additional 91% conversion to dimethyl ether                     

                                      TABLE 2                                     __________________________________________________________________________              Example                                                                       5  6  7   8  9   10 11 12 13                                        __________________________________________________________________________    Aliphatics                                                                    C.sub.1   3  3  3   2  3   1  1  5  5                                         C.sub.2 's                                                                              3  3  3   3  6   2  2  5  5                                         C.sub.3 's                                                                              53 60 69  59 50  66 66 59 60                                        C.sub.4 's                                                                              18 16 7   14 20  18 11 11 12                                        C.sub.5 's-C.sub.11 's                                                                  3  13 trace                                                                             2  5   3  2  2  1                                         Aromatics                                                                     C.sub.6 -C.sub.14 's                                                                    20 5  18  20 16  10 18 18 17                                        Conversion                                                                              97 95 100 96 73  92 99 98 99                                        Zeolite Form                                                                            Cu Ag Sn  Sn Ti  Ga Ga Cu Ti                                        Temp/°C.                                                                         327                                                                              327                                                                              327 327                                                                              327 327                                                                              327                                                                              377                                                                              377                                       GHSV/h.sup.-1                                                                           111                                                                              85 60  211                                                                              200 50 64 327                                                                              200                                       iso-content                                                                             52 59 42  43 45  43 44 46 39                                        aliphatic content                                                                       79 95 81  84 82  93 85 80 81                                        __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________    FEED COMPOSITION (% v/v)                                                           monochloro-                                                                          monobromo-                                                                           dichloro-                                                                          monochlo-                                             Example                                                                            methane                                                                              methane                                                                              methane                                                                            ethane nitrogen                                                                           hydrogen                                  __________________________________________________________________________    14   70     --     --   30     --   --                                        15   --     100    --   --     --   --                                        16   50     --     --   --     --   50                                        17   96     --     4    --     --   --                                        18   91     --     9    --     --   --                                        19   82     --     18   --     --   --                                        Comp 57     --     43   --     --   --                                        Test C                                                                        Comp --     --     18   --     82   --                                        Test D                                                                        __________________________________________________________________________

                  TABLE 4                                                         ______________________________________                                               Example                                                                       14   15     16     17   18   19   C    D                               ______________________________________                                        Aliphatics                                                                    C.sub.1   1      3      2    6    2    2   --   --                            C.sub.2 's                                                                              4      8      4    6    3    3   --   --                            C.sub.3 's                                                                             49     55     73   78   77   69   --   --                            C.sub.4 's                                                                             24     15     16    5   10   11   --   --                            C.sub.5 's-C.sub.11 's                                                                  5      3      2    0    0    1   --   --                            Aromatics                                                                     C.sub.6 -C.sub.14 's                                                                   16     16      3    5    8   14   --   --                            Conversion                                                                             85     58     94   96   99   93    0    0                            Zeolite Form                                                                           Ga     Ga     Sn   Sn   Sn   Sn   Sn   Sn                            Temp/°C.                                                                        327    327    327  327  327  327  327  327                           GHSV/h.sup.-1                                                                          170    200    258  64   61   214  177  217                           ______________________________________                                    

                                      TABLE 5                                     __________________________________________________________________________                EXAMPLE                                                                             Comp                                                                          Test                                                        PRODUCT     20    A     21    22   23   24                                    __________________________________________________________________________    Aliphatics                                                                    C.sub.1     29.9  trace 36.8  20.6 14.5 35.4                                  C.sub.2 's  6.0   trace 22.3  14.4 22.6 13.0                                  C.sub.3 's  20.8  7.6   28.0  36.0 40.0 35.2                                  C.sub.4 's  33.3  68.2  4.8   20.1 15.1 11.4                                  C.sub.5 -C.sub.8 's                                                                       10.0  24.1  4.7   8.9  7.7  5.0                                   Monochloroethane                                                                          0     0     3.0                                                   % Monochloromethane                                                                       42    7     52    23   58   77                                    conversion                                                                    Zeolite type                                                                              Theta-1                                                                             ZSM-5 Theta-1                                                                             Theta-1                                                                            Theta-1                                                                            Theta-1                               Form        Hydrogen                                                                            Hydrogen                                                                            Hydrogen                                                                            zinc tin  titanium                              Temperature (°C.)                                                                  227   227   500   327  377  377                                   GHSV (h.sup.-1)                                                                           37    57    80    38   43   40                                    __________________________________________________________________________

We claim:
 1. A process for the conversion of a monohalomethaane to aproduct comprising hydrocarbons having at least 2 carbon atoms whichprocess comprises contacting the monohalomethane at elevated temperaturewith a synthetic crystalline aluminosilicate zeolite having a silica toalumina molar ratio of at least 12:1 and containing cations of hydrogenions, which cations are introduced either by exchange and/or deposition,andwherein the zeolite is Theta-1.
 2. A process according to claim 1wherein the elevated temperature is in the range 80° to 600° C.
 3. Aprocess according to claim 2 wherein the temperature is below about 330°C. and the hydrocarbon product predominantly comprises aliphatichydrocarbons.
 4. A process according to claim 3 wherein the temperatureis in the range 200° to 330° C.
 5. A process according to claim 1wherein the monohalomethane is obtained by halogenation oroxyhalogenation of methane in admixture with ethane and/or propane.
 6. Aprocess according to claim 1 wherein the monohalomethane ismonochloromethane.
 7. A process according to claim 4, wherein thetemperature is in the range of 200° to 260° C.